How to create a block ON the correct side of another block where the special arrow hits

I want to make a flare gun from "Deep Rock Galactic" and redo the "torch arrow mod" that hasn't been updated in five years, but I can't figure out how to make the flares spawn on the side of the block they hit . I made the signal block and projectile two separate objects. The trigger/object coordinates are the XYZ of the block it hit. I think I should determine which side the projectile hits the block from and place the block ON that side with, as example "place block at x(+1), y, z" , but I can't figure out how.

Also, I apologize for the mistakes in text. I still use a translator to write properly in English.